JPH05225975A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To improve initial discharge capacity, and reduce charging and discharging cycles necessary for initial activation to improve productivity by using hydrogen storage alloy particles after treatment and removal of an oxide film with hydrochloric acid. CONSTITUTION:Each powder of Misch metal, nickel, cobalt and aluminum is so measured and mixed as to obtain the predetermined composition ratio, dissolved under heating by an arc melting method, and cooled, thereby forming a hydrogen storage alloy ingot. Thereafter, the ingot is pulverized to form hydrogen storage alloy powder comprising grains of 250-mesh size or less. Then, the alloy powder is immersed in hydrochloric acid having the predetermined concentration, a trace of oxide films generated on the surface of the alloy, for example, films of lanthanum oxide, lanthanum hydroxide, or the like is removed and, then, the alloy is subjected to a washing and drying process. A hydrogen storage alloy electrode comprising the hydrogen storage alloy particles after treatment and removal of the oxide film with hydrochloric acid is improved in initial discharge capacity at the time of manufacturing an H-M battery, and the number of charging and discharging cycles necessary for initial activation can be reduced, thereby enabling productivity to be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode used for a negative electrode of a nickel-hydrogen battery or the like.

[0002]

2. Description of the Related Art Conventionally, a nickel-hydrogen battery having a large energy density, which uses an electrode using a hydrogen storage alloy as a negative electrode of a secondary battery, uses nickel oxide for the positive electrode, and uses an alkaline aqueous solution as an electrolyte. Proposed. In this case, the hydrogen storage alloy for the negative electrode is, for example, LaNi ₅ series alloy, MmNi ₅ series alloy, and the like, powders of plural kinds of metals of respective composition elements are weighed and mixed at a predetermined composition ratio, and the mixed powder is arc-melted. After being heated and melted by the method, it is cooled to form an ingot, which is mechanically crushed to obtain a hydrogen storage alloy powder of 250 mesh or less. The hydrogen storage alloy powder thus obtained is mixed with a conductive agent powder and a binder to form a mixture, which is pressed onto a porous substrate such as a nickel wire mesh to produce a hydrogen storage alloy electrode, which is used as a negative electrode. As a sealed nickel-hydrogen battery.

[0003]

The hydrogen-absorbing alloy constituting the hydrogen-absorbing alloy electrode obtained by the above conventional manufacturing method is generally prepared by the initial activation of the battery, that is, in a state in which a stable capacity can be taken out. It is necessary to develop a hydrogen storage alloy electrode that requires several cycles of charge and discharge until it becomes a reality, and can reduce the number of required cycles.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a hydrogen storage alloy electrode satisfying the above demands, which comprises hydrogen storage alloy particles treated with hydrochloric acid.

[0005]

In the hydrogen storage alloy electrode of the present invention, the particles of the hydrogen storage alloy which are the main constituents of the hydrogen storage alloy electrode have the oxide film on the surface thereof already removed by the treatment with hydrochloric acid. At this time, the initial discharge capacity increases and the number of charge / discharge cycles required for initial activation decreases.

[0006]

EXAMPLES Examples of the present invention will be described in detail. The hydrogen storage alloy material, which is the main component of the hydrogen storage alloy electrode of the present invention, may be of any type such as LaNi-based alloy or MmNi-based alloy. In short, the hydrogen storage alloy particles constituting the hydrogen storage alloy electrode of the present invention, the surface is subjected to hydrochloric acid treatment,
That is, the oxide film formed on the surface is removed. The treatment for removing the oxide film can be performed at any stage in the manufacturing process of the hydrogen storage alloy electrode. As a typical example, at the stage of pulverizing a hydrogen storage alloy ingot having a predetermined composition to obtain a hydrogen storage alloy powder,
The alloy powder is immersed in hydrochloric acid having a predetermined concentration to remove the oxide film formed on the surface of the alloy, for example, a small amount of lanthanum oxide or lanthanum hydroxide, or immediately using the above alloy powder. A mixture is prepared, which is pressure-bonded to a porous collector plate to produce an electrode, which is then immersed in hydrochloric acid to remove the oxide film on the surface of alloy particles constituting the electrode with the hydrochloric acid. Can be considered. In any of the above cases, after the hydrochloric acid immersion treatment, washing with water and drying are performed.

Next, the embodiment will be described. Example 1 Commercially available powders of misch metal, nickel, cobalt, and aluminum were mixed in a predetermined composition ratio, for example, MmNi _4.0 C.
o _0.5 Al _0.5 were weighed and mixed, these were heated and melted by an arc melting method, and cooled to obtain a hydrogen storage alloy ingot. Next, this was pulverized to obtain a hydrogen storage alloy powder composed of particles of 250 mesh or less. next,
Carbonyl nickel powder as a conductive agent was added to the alloy powder in an amount of 15 wt. %, 5 wt.% Of tetrafluoroethylene powder as a binder. % And mixed, and this mixture was pressed onto a nickel wire mesh as a porous current collector plate to produce a plate-shaped hydrogen storage alloy electrode. According to the present invention, the electrode is immersed in 0.5N hydrochloric acid for 30 minutes at room temperature, then washed with water and dried to form a hydrogen storage alloy electrode A comprising hydrogen storage alloy particles from which the oxide film of the present invention is removed. did. For comparison, the hydrogen storage alloy electrode manufactured by the above-mentioned conventional method without such hydrochloric acid treatment was used as a reference electrode B. The weight of the hydrogen storage alloy particles in both electrodes manufactured in this way was about 1 g. Each of these electrodes was used as a negative electrode, and a nickel plate was combined as a counter electrode. % Of potassium hydroxide aqueous solution were used to prepare open test cells A'and B '. Using these test cells A'and B ', the capacity that can be taken out by the first charge and discharge was confirmed. The charge and discharge were repeated for each of them, and the number of charge and discharge cycles required until the capacity became stable was examined.
Charge / discharge is performed at 6 mA / cm in each of the test cells A ′ and B ′.
After charging with the ^second current density up to 130% of the electrochemical hydrogen storage capacity of the hydrogen storage alloy electrode, the voltage of the hydrogen storage alloy electrode at a current density of 10 mA / cm ² is -0.75Vvs. H
It was carried out by discharging until g / HgO was reached. The above charge / discharge test results are shown in Table 1 below.

[0008]

[Table 1]

As is clear from Table 1, the battery using the hydrogen storage alloy electrode of the present invention which has been subjected to the hydrochloric acid treatment, is compared with the battery using the conventional storage alloy electrode which is not subjected to the hydrochloric acid treatment, It can be seen that the initial discharge capacity increases and the number of charge / discharge cycles between initial activations decreases.

Although the above-mentioned hydrochloric acid treatment was carried out at room temperature, it is effective to shorten the treatment time by appropriately heating the hydrochloric acid and raising the treatment temperature appropriately. If the oxide film on the surface of the alloy to be treated is easily removed, hydrochloric acid can be diluted with water and used. Depending on the type of hydrogen storage alloy to be treated, the concentration of hydrochloric acid should be increased to use. ..

Example 2 The hydrogen-absorbing alloy powder immediately after pulverization obtained in the same manner as in Example 1 was immersed in the above 0.5N hydrochloric acid at room temperature for 30 minutes, then washed with water and dried. Thus, a hydrogen storage alloy powder composed of hydrogen storage alloy particles from which the oxide film formed on the surface was removed was obtained. Thus, a hydrogen storage alloy powder that was treated with hydrochloric acid was obtained. Next, using this, the hydrogen storage alloy electrode of the present invention was manufactured in the same manner as above. Using this as a negative electrode, the same test cell as above was manufactured. When this test cell was repeatedly charged and discharged in the same manner as above, the same result as shown in Table 1 was obtained in the same manner as in the test cell A ′.

[0012]

As described above, the hydrogen storage alloy electrode composed of the hydrogen storage alloy particles whose oxide film has been subjected to the removal treatment with hydrochloric acid is used as a negative electrode in an H-metal alloy such as a hydrogen-nickel battery.
When manufacturing M batteries, improve the initial discharge capacity,
Further, the number of charge / discharge cycles required for initial activation is reduced, and the productivity is improved.

Claims (1)

[Claims] 1. A hydrogen storage alloy electrode comprising hydrogen storage alloy particles treated with hydrochloric acid.